| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Robert Haas <robertmhaas(at)gmail(dot)com>, jd(at)commandprompt(dot)com, Thom Brown <thom(at)linux(dot)com>, Bruce Momjian <bruce(at)momjian(dot)us>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Dave Page <dpage(at)pgadmin(dot)org>, Peter Eisentraut <peter_e(at)gmx(dot)net>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: Configuring synchronous replication |
| Date: | 2010-09-24 11:12:29 |
| Message-ID: | 4C9C879D.6090702@enterprisedb.com |
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| Lists: | pgsql-committers pgsql-hackers |
On 24/09/10 13:57, Simon Riggs wrote:
> If you want high availability you need N+1 redundancy. If you want a
> standby server that is N=1. If you want a highly available standby
> configuration then N+1 = 2.
Yep. Synchronous replication with one standby gives you zero data loss.
When you add a 2nd standby as you described, then you have a reasonable
level of high availability as well, as you can continue processing
transactions in the master even if one slave dies.
> Show me the textbook that describes what happens with 2 standbys. If one
> exists, I'm certain it would agree with my analysis.
I don't disagree with your analysis about multiple standbys and high
availability. What I'm saying is that in a two standby situation, if
you're willing to continue operation as usual in the master even if the
standby is down, you're not doing synchronous replication. Extending
that to a two standby situation, my claim is that if you're willing to
continue operation as usual in the master when both standbys are down,
you're not doing synchronous replication.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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